1. Field of the Invention
The present invention relates to a mobile communication system for carrying out multicast communication by a radio station (a radio control unit or a base station) and a plurality of mobile stations, a mobile communication method, and a radio station suitably used for the same.
Specifically, the present invention relates to a mobile communication system in which a specific base station transmits common information to a plurality of mobile stations, a mobile communication method, and a radio station suitably used for the same.
2. Description of the Related Art
As shown in FIG. 1, broadcast communication whereby one or a plurality of base stations 100a to 100g transmit common information to unspecified mobile stations 200a to 200l in predetermined areas 300a to 300g all at once is known in a conventional mobile communication system.
As shown in FIG. 2, multicast communication whereby one or a plurality of base stations 100a to 100g transmit common information to a plurality of mobile stations joining in (belonging to) a specific group in predetermined areas 300a to 300l all at once is known in a conventional mobile communication system.
However, there is a problem in that communication quality varies from one mobile station to another, so that it is impossible to satisfy desired communication quality at certain mobile stations in the conventional mobile communication systems.
For example, a mobile station located near the base station can obtain better communication quality than other mobile stations. However, other mobile stations can obtain only poor communication quality compared with the mobile station located near the base station.
In other words, there is a problem in that communication quality changes depending on a positional relationship between the base station and each of the mobile stations existing within the same area, so that the communication quality is not uniform among the mobile stations. Therefore, there has been demand for development of a mobile communication system which can provide desired communication quality to all the mobile stations existing within the same area.